Field of the Invention
The present invention relates to a unidirectional microphone, and more particularly relates to a unidirectional microphone that can realize unidirectivity while preventing deterioration in sound quality.
Description of the Related Art
Bi-directional ribbon microphones have been considered to have good sound quality, and enable obtainment of a favorable directional frequency response in a frequency band from a low resonant frequency and higher because the microphone is mass controlled.
However, use of a long damping acoustic tube is needed for realization of unidirectivity or non-directivity. Further, since the damping acoustic tube has a finite length, obtainment of the favorable directional frequency response is difficult.
Meanwhile, unidirectional condenser microphones can enable the favorable directional frequency response even with small size.
Therefore, realization of the bi-directional ribbon microphones having unidirectivity with good sound quality has been desired. Further, realization of the unidirectivity can suppress occurrence of howling at a time of amplification.
Conventionally, it is known that the unidirectivity is obtained by summing an output of a bi-directional ribbon microphone element and an output of a non-directional condenser microphone element.
That is, when the output of the bi-directional ribbon microphone element illustrated in the graph of directional frequency characteristics of FIG. 6A and the output of the non-directional condenser microphone element of the graph of directional frequency characteristics of FIG. 6B are added, then, unidirectional characteristics with a large output in a 0° direction is obtained, as illustrated in FIG. 6C.
In Japanese Unexamined Patent Application No. 2015-111812 A, the applicant of the present application discloses a stereo microphone including one non-directional condenser microphone unit and two bi-directional ribbon microphone units. In the stereo microphone, directional axes of the two bi-directional ribbon microphone units are arranged to form a predetermined angle with respect to a central axis of a directional axis of the stereo microphone in the same plane, and an acoustic terminal of the non-directional condenser microphone unit is arranged close to acoustic terminals of the bi-directional ribbon microphone units.
According to this configuration, the stereo microphone can provide excellent directional frequency characteristics.
However, in a case of the configuration where the output of the bi-directional ribbon microphone element and the output of the non-directional condenser microphone element are added to obtain the unidirectivity, a problem that the sound quality is deteriorated by adding arises, because half of the output illustrated in FIG. 6C is an audio signal from the non-directional condenser microphone.